This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study addresses Grand Challenge #6 of the Global Health Initiative: Learn which immunological responses provide protective immunity (against HIV-1). Identification of full-length transmitted HIV-1 genomes could be instrumental in HIV-1 pathogenesis, microbicide, and vaccine research by enabling direct analysis of those viruses actually responsible for productive clinical infection. We have shown in 12 acutely infected subjects (9 clade B and 3 clade C) that complete HIV-1 genomes of transmitted/founder viruses can be inferred by single genome amplification and sequencing of plasma virion RNA. This allowed for molecular cloning and biological analysis of transmitted/founder viruses and comprehensive genome-wide assessment of the genetic imprint left on the evolving virus quasispecies by a composite of host selection pressures. Transmitted viruses encoded intact canonical genes (gag-pol-vif-vpr-tat-rev-vpu-env-nef) and replicated efficiently in primary human CD4(+) T lymphocytes but much less so in monocyte-derived macrophages. Transmitted viruses were CD4 and CCR5 tropic and demonstrated concealment of coreceptor binding surfaces of the envelope bridging sheet and variable loop 3. At 2 mo after infection, transmitted/founder viruses in three subjects were nearly completely replaced by viruses differing at two to five highly selected genomic loci;by 12-20 mo, viruses exhibited concentrated mutations at 17-34 discrete locations. These findings reveal viral properties associated with mucosal HIV-1 transmission and a limited set of rapidly evolving adaptive mutations driven primarily, but not exclusively, by early cytotoxic T cell responses. We have recently described two autologous monoclonal antibodies, 6.4C and 13.6A, generated from a Zambian subject, that each recognize a V1V2-dependent target on the founder Env. Using these Mabs, we identified two mutations in the V1V2 domain that were involved in escape at the single antibody level. We have extended these studies to test whether a change in glycosylation is necessary for Nab resistance and to further define epitopes of the Mabs.